How to find all dates from the present and previous month?

Question

I have a table

EmployeeSalary:

Date       | Salary
01.12.2016 | 2000
01.02.2016 | 3000
03.02.2016 | 5000
01.03.2017 | 1000
30.01.2017 | 5000
10.03.2017 | 1300

When the System Date is 13.03.2017. How to get the present month dates and the past month Dates (i.e., from February 1 to System date).

My code is :

start= format(Sys.Date() - 30, '%Y-%m-01') 
end=Sys.time() 
while (start<end)
{
  print(EmployeeSalary)
  EmployeeSalary$"Date" = EmployeeSalary$"Date"+1
}

Error which I get:

Error: non-numeric argument to binary Operator

Expected Output is :

EmployeeSalary:

Date       | Salary
01.02.2016 | 3000
03.02.2016 | 5000
01.03.2017 | 1000
10.03.2017 | 1300

I didn't understood what you need, but you can use seq() function with dates, ie, seq(Sys.Date(), by='month', length=3) outputs "2017-03-13" "2017-04-13" "2017-05-13". — Fernando
To convert your date variable to an R Date-type , you can use as.Date. For example, as.Date("01.12.2016", "%m.%d.%Y") will return a date for the first cell. — lmo
this command gives the sequence of months. But I Need the previous month and present month salary Details as mentioned in the EmployeeSalary table — Mathumathi Anblagan

Dirk Eddelbuettel Dirk Eddelbuettel · Accepted Answer · 2017-03-13T14:04:48

Here is one way:

R> dates <- seq(Sys.Date(), length=62, by=-1)
R> mon <- function(d) as.integer(format(d, "%m")) %% 12
R> dates[mon(dates) >= mon(Sys.Date())-1]
 [1] "2017-03-13" "2017-03-12" "2017-03-11" "2017-03-10" "2017-03-09"
 [6] "2017-03-08" "2017-03-07" "2017-03-06" "2017-03-05" "2017-03-04"
[11] "2017-03-03" "2017-03-02" "2017-03-01" "2017-02-28" "2017-02-27"
[16] "2017-02-26" "2017-02-25" "2017-02-24" "2017-02-23" "2017-02-22"
[21] "2017-02-21" "2017-02-20" "2017-02-19" "2017-02-18" "2017-02-17"
[26] "2017-02-16" "2017-02-15" "2017-02-14" "2017-02-13" "2017-02-12"
[31] "2017-02-11" "2017-02-10" "2017-02-09" "2017-02-08" "2017-02-07"
[36] "2017-02-06" "2017-02-05" "2017-02-04" "2017-02-03" "2017-02-02"
[41] "2017-02-01"
R>

We create sequence of dates going backwards. We then create helper function to get the (integer-valued) month for a date.

Given those two, we index the date sequence down to the ones matching your criteria: from this months or the preceding month.

And by taking 'month modulo 12' we also catch the case of January comparing to December.

How to find all dates from the present and previous month?

1 Answers